This invention relates to a method of testing seams between adjacent layers of plastic material, and in particular to a method of testing parallel, welded seams between adjacent layers of polyethylene.
During the past few years, because of environmental concerns, there has been a tremendous increase in the use of impervious sheet material for containing waste. The sheet material most suitable at this time for containing waste liquids is polyethylene which is extremely inert to most chemicals.
Because polyethylene is inert, the material cannot be glued, and all seams must be welded, i.e. the overlapping plastic sheets are partially melted and thus fused together. Obviously, the finished product is only as good as the welded seams.
There are two basic welding techniques currently in use, extrusion welding and heat fusion welding. Both welding techniques are capable of producing quality welds having strengths equal to that of the basic plastic material. By the same token, incompetent operators, inferior equipment or adverse conditions can result in flawed welds which are weaker than the plastic.
It is currently required that welded seams between adjacent sheets of material, e.g. polyethylene, be tested for leaks using vacuum, ultrasonic or low pressure are techniques.
In the conventional method of testing, the quality of the weld is determined by cutting out coupons from the weld seam for "peel" testing on a tensometer. There are however two major flaws to this method. Firstly, by cutting out the coupon, a hole in a good seam is created and future leakage at the resulting patch is a distinct possibility. Secondly, the quality of the weld is only checked at the point where the coupon is removed, the rest of the seam is assumed to be flawless.
A need exists therefore for a relatively simple method of determining the strength and integrity of a welded seam along the entire length of the seam.